<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>事件发布订阅模式</title>
</head>
<body>
  <script>
    //模拟vue的事件发布订阅，忽略参数
    class EventEmitter {
      constructor () {
        // { 'click':[fn1,fn2], 'change': [fn]}
        this.subs = {}
      }

      // 注册事件
      $on (eventType,handler) {
        this.subs[eventType] = this.subs[eventType] || []
        this.subs[eventType].push(handler)
      }

      // 触发事件
      $emit (eventType) {
        if (this.subs[eventType]){
          this.subs[eventType].forEach(handler => {
            handler()
          })
        }
      }
    }

    //测试
    let em = new EventEmitter;
    em.$on('click', () => {
      console.log('click1')
    })
    em.$on('click', () => {
      console.log('click2')
    })
    em.$emit('click')
  </script>
</body>
</html>